A common type of vacuum cleaner generally comprises a motor that drives a fan to generate an air flow, and a collection vessel. In use, the collection vessel removes dirt and debris from the flow of air and the air is then expelled out to the atmosphere through an exhaust port.
Vacuum cleaners generally produce a lot of noise from the air flow and the motor. In most cases, the noise is mainly radiated by the nozzle and the housing of the vacuum cleaner. One of the paths for the noise to get out of the housing is via the exhaust channel. Due to the acoustically “hard” walls of the exhaust channel, a large part of the noise energy is reflected out of the canister, resulting in a high noise level of the total vacuum cleaner.
Counter measures are known to reduce the noise output, but many increase the flow resistance and/or take up a lot of space within the housing. It is known to provide acoustical absorption material inside the motor housing/compartment, and/or in the exhaust channel to reduce the noise.
It is known from U.S. Pat. No. 5,289,612 to reduce the noise of the fan and motor that the user is subjected to by utilising a muffler. The muffler is positioned over the end of an exhaust port, and is formed from a series of baffles that are configured to decrease the energy, and therefore, the noise, of the exhaust air. It has been found that using a muffler to decrease the energy of the exhaust air to reduce the noise emanating from the exhaust may also reduce the suction pressure produced by the fan, and, therefore, reduce the efficiency of the vacuum cleaner and its ability to clean.
DE102010039483 discloses a device for sound attenuation in air currents, in which a length of an edge of a sound-damping element is enlarged by means of alternating projections and recesses, so that a speed of an air flow on the edge is substantially reduced, whereby turbulence of the air flow is reduced, thus reducing the sound emission produced by the air flow.